1. Field of the Invention
The invention relates to storage tanks generally and more particularly to vacuum testing risers for storage tanks.
2. Related Art
Storage tanks are used to store a wide variety of materials. Storage tanks are often located underground to conserve space. Special concern arises when such underground storage tanks are used to store environmentally hazardous materials. For example, underground storage tanks are often used to store gasoline and other petroleum products. Underground storage tanks are also used to store hazardous chemicals or other manufacturing liquid waste and sewage (such tanks are often referred to as wastewater storage tanks). Because of the nature of these materials, concern about leaks in underground storage tanks has lead many municipalities to pass laws requiring leak detection and secondary containment systems. Even in situations where there are no laws governing underground storage tanks containing environmentally hazardous materials, concern for the environment has led many to take some or all of the aforementioned precautions in connection with their tanks.
The aforementioned concerns have led to the introduction of water resistant and watertight riser and cover systems in the last few years for access to and protection of the manway and/or pipe/tank connections. An example of a watertight riser and cover system is disclosed in U.S. Pat. No. 5,595,456, which is commonly owned by the assignee of the present invention. The motivation for providing a watertight riser and lid system is that many times the connection between the tank and a supply line passes through the riser, and it is possible for a leak to develop in such a connection.
To date, there are no known regulations concerning the watertightness of a riser and lid system. Testing the watertightness of a riser and lid system is complicated by the fact that the riser and lid system must be installed on-site rather than at the factory.
Fibrelite has developed a complicated and expensive system that must be installed along with the original installation of their system. A serious drawback to the Fibrelite system is that it appears to require that the actual riser lid be replaced with a special test cover. Thus, the Fibrelite system does not test the actual riser lid seals.
What is needed is a simple and economical method and apparatus for periodically testing the watertightness of watertight riser and lid assemblies, particularly those that are already installed throughout the country.
The present invention meets the foregoing need to a great extent by providing a simple method and apparatus for detecting leaks in watertight riser and lid system. This can be used for water resistant systems by adding the water tight lid. A difference in pressure (preferably a vacuum created on the inside of the riser) between the inside of the riser and lid assembly and the outside is created and monitored to insure that no leaks exist. The inside of the riser assembly is then monitored for a set period of time to insure that the total change in pressure does not exceed a threshold. In a highly preferred embodiment, an apparatus automatically creates the desired vacuum and then isolates a vacuum gauge to monitor the vacuum in the riser. Methods for isolating a leak are also presented in the event that a leak is detected.